Color Liquid Crystal Display Apparatus

ABSTRACT

Disclosed is a color liquid display (LCD) employing a transmissive color liquid display panel. The display includes a complementary color light emitting diode, which is one of a cyan light emitting diode ( 21 C), emitting cyan light, a yellow light emitting diode, emitting yellow light, and a magenta light emitting diode, emitting magenta light, in addition to light emitting diodes emitting three prime colors, as a light source. The display also includes a complementary color filter, having at least one of a cyan filter CFC having a transmission wavelength range corresponding to the cyan light, a yellow filter CFY having a transmission wavelength range corresponding to the yellow light and a magenta filter CFM having a transmission wavelength range corresponding to the magenta light, in addition to a tristimulus color filer, as a color filter ( 19 ).

TECHNICAL FIELD

This invention relates to a color liquid crystal display (LCD) apparatuswith which the color gamut can be made broader to assure more faithfulcolor reproducing performance.

The present application claims priority rights on the basis of theJapanese Patent Application 2004-294242 filed in Japan on Oct. 6, 2004.The contents of these Patent Applications are to be incorporated byreference in the present application.

BACKGROUND ART

Among standard color spaces for computer display, there is the sRGBstandard prescribed by IEC (International Electro-technical Commission).This standard gives a definition on the relationship between a videosignal RGB and the calorimetric values by having chromaticity points ofthree prime colors of red (R), green (G) and blue (B) coincide with thecolorimetric parameters of Rec.709 recommended by ITU-R (InternationalTelecommunication Union Radio communication). In a display apparatus,complying with this sRGB standard, if a video signal RGB is applied, thecolorimetrically same color may be displayed.

Meanwhile, with a picture unit, receiving and displaying the colorinformation, captured by a camera or a scanner, such as a display or aprinter, it is essential to demonstrate the received color informationaccurately. For example, if a camera has captured the color informationaccurately, but a display demonstrates the color information onlyinappropriately, color reproduction performance of the system on thewhole is deteriorated.

In a current standard monitor device, the display is prescribed by thecolor gamut of the sRGB standard. In actuality, there are many colorsbeyond the color gamut of sRGB, such that there are object colors thatcannot be represented by a standard monitor device complying with thesRGB standard. For example, with a halide film used in a camera, or witha digital camera printer, the range of sRGB has already been exceeded.If the broad dynamic range is procured, and an image pickup operation iscarried out correctly, there are produced object colors that cannot berepresented on a standard monitor device of the sRGB standard.

The sYCC, having a color space broader than that of sRGB, has beenadopted as a standard by business circles, in order to cope with thecolor gamut which has become broader. The sYCC has derived, from thesRGB, the luminance difference color difference separation space, usingITU-R BT.601, which is the international standard of a transformationmatrix from RGB to YCC as defined for high vision television. The colorgamut of sYCC is broader as the color space, such that, with the sYCC,the color outside sRGB can be represented.

On the other hand, in the NTSC system, adopted as the broadcast systemfor color television, the bandwidth is broader than in sRGB. If sYCC isto be implemented, the color gamut on the display with sYCC needs to beequivalent to or even exceed that of the NTSC system on a display.

On the other hand, a TV receiver of an extremely thin thickness, such asa liquid crystal display (LCD) or a plasma display panel (PDP), has beendeveloped and put to practical use, to take the place of the cathode raytube (CRT) which has long been used since the start of TV broadcasting.In particular, a color liquid crystal display, employing a color liquidcrystal display panel, is expected to become popular at a rapid ratebecause it permits driving with low power consumption and thelarge-sized color liquid crystal display panel has become lessexpensive.

As for the color liquid crystal display apparatus, the backlight system,in which a transmissive color liquid crystal display panel isilluminated from its backside with a backlight device to display a colorpicture, is in the mainstream. The light source, preferentially used forthe backlight device, is a CCFL (Cold Cathode Fluorescent Lamp),emitting white light using a fluorescent tube.

In general, in a transmissive color liquid crystal display apparatus, acolor filter, employing a tristimulus filter of spectralcharacteristics, shown for example in FIG. 1, made up of a blue filterCFBo (460 nm), a green filter CFGO (530 nm) and a red filter CFRo (685nm), where the numbers entered in parentheses denote the peaktransmission wavelength of each filter, is provided from one pixel ofthe color liquid crystal display panel to another.

On the other hand, the white light, emitted from a three-wavelengthCCFL, used as a light source for a backlight device of the color liquidcrystal display apparatus, has a spectrum shown in FIG. 2, such that itcontains light of different intensities in a variety of wavelengths.

Hence, there is a problem that the color reproduced by the combinationof the backlight device, having such CCFL, emitting the light of threewavelength ranges, as light source, and the color liquid crystal displaypanel, having the color filter, described above, is rather poor in colorpurity.

FIG. 3 shows the color reproducing range of the color liquid crystaldisplay apparatus, including the backlight device, having theabove-described three-wavelength CCFL as a light source. Specifically,FIG. 3 depicts an xy chromaticity diagram of the XYZ color system, asprescribed by the Commission Internationale de l'Eclairage (CIE).

As may be seen from FIG. 3, the color reproducing range of the colorliquid crystal display apparatus, having the backlight device, employingthe CCFL as light source, is narrower than the color reproducing rangeprovided for by the standard of the NTSC (National Television SystemCommittee) system adopted as the color television broadcasting system.That is, the former color reproducing range may not be said to copesufficiently with the current television broadcasting.

On the other hand, there is a fear that the CCFL, containing mercury inthe phosphorescent tube, may have an ill effect on the environment.Hence, a demand is raised for a light source that may take the place ofthe CCFL as a light source of the backlight device. With the developmentof the blue light emitting diode, the light emitting diodes, emittinglight of three prime colors, namely red light, green light and bluelight, are now in order. Thus, with the use of the light emitting diodesas light source for the backlight device, the color light obtained bythe color liquid crystal display panel may be improved in color purity,and hence it may be expected that the color reproducing range may bemade as broad as or even broader than the color reproducing rangeprovided for by the NTSC system.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, there is a problem that the color reproducing range of thecolor liquid crystal display apparatus, employing a backlight device,having light emitting diodes as light source, is not as yet broad enoughto meet the color reproducing range prescribed by the NTSC system.

When light emitting diodes of three prime colors are used as lightsources, the color reproducing range depends mainly on the wavelengthbands of the light emitting diodes. If desired to enlarge the colorgamut further, it is also crucial to optimize the transmissionwavelength bands of the color filter, provided on the color liquidcrystal display panel, in order to cope with the wavelength bands of thelight emitting diodes. That is, the color purity of a picture displayedon a color liquid crystal display apparatus is appreciably changed bythe matching between the light emitting diodes, used as light sources,and the color filter, such as to affect the color reproducing rangeappreciably. Hence, the optimum designing of the light emitting diodes,as light source, and the color filter, represents a crucial factor forachieving the wide color gamut.

In view of the above problems, it is an object of the present inventionto provide a color liquid crystal display apparatus of the backlightsystem in which characteristics of the light emitting diode and thecolor filter may be optimized to allow for a broader color gamut.

The present invention provides a color liquid crystal display apparatusincluding a transmissive color liquid crystal display panel, having acolor filter, and a backlight device for illuminating the color liquidcrystal display panel with white light from a backside thereof, thebacklight device including: a light source made up of light emittingdiodes emitting three prime colors, namely a red light emitting diode,emitting red light having a peak wavelength λpr such that 640 nm≦λpr≦645nm, a green light emitting diode, emitting green light having a peakwavelength λpg such that 525 nm≦λpg≦530 nm, and a blue light emittingdiode, emitting blue light having a peak wavelength λpb such that 440nm≦λpb≦450 nm, and one or more of complementary color light emittingdiodes including at least one of a cyan light emitting diode, emittingcyan light, a yellow light emitting diode, emitting yellow light and amagenta light emitting diode, emitting magenta light; and color mixingmeans for mixing the color light emitted from the light source togenerate white color, wherein the color filter includes a tristimuluscolor filter, made up of a red filter, a green filter and a blue filter;the red filter having a peak wavelength λpr of a transmission wavelengthrange such that 685 nm≦λpr≦690 nm, and having zero transmittance for thetransmission wavelength range of the blue filter; the green filterhaving a peak wavelength λpg of a transmission wavelength range of 530nm and a half value width Fhwg of the transmission wavelength range suchthat 80 nm≦Fhwg≦100 nm; the blue filter having a peak wavelength Fpb ofa transmission wavelength range such that 440 nm≦Fpb≦460 nm, and thecolor filter further includes one or more complementary color filtersincluding at least one of a cyan filter of a transmission wavelengthrange corresponding to cyan light, a yellow filter of a transmissionwavelength range corresponding to yellow light and a magenta filter of atransmission wavelength range corresponding to magenta light.

According to the present invention, as a light source for a backlightdevice, a light source made up of light emitting diodes emitting threeprime colors and one or more of complementary color light emittingdiodes are used. The light emitting diodes emitting three prime colorsare a red light emitting diode, emitting red light having a peakwavelength λpr such that 640 nm≦λpr≦645 nm, a green light emittingdiode, emitting green light having a peak wavelength λpg such that 525nm≦λpg≦530 nm, and a blue light emitting diode, emitting blue lighthaving a peak wavelength λpb such that 440 nm≦λpb≦450 nm. The one ormore of complementary color light emitting diodes include at least oneof a cyan light emitting diode, emitting cyan light, a yellow lightemitting diode, emitting yellow light and a magenta light emittingdiode, emitting magenta light.

As a color filter for a color liquid crystal display panel, atristimulus color filter and one or more complementary color filters areused. The tristimulus color filter is made up of a red filter, a greenfilter and a blue filter. The red filter has a peak wavelength Fpr of atransmission wavelength range such that 685 nm≦Fpr≦690 nm, and has zerotransmittance for the transmission wavelength range of the blue filter.The green filter has a peak wavelength Fpg of a transmission wavelengthrange of 530 nm and a half value width Fhwg of the transmissionwavelength range such that 80 nm≦Fhwg≦100 nm. The blue filter has a peakwavelength Fpb of a transmission wavelength range such that 440nm≦Fpb≦460 nm. The one or more complementary color filters include atleast one of a cyan filter of a transmission wavelength rangecorresponding to cyan light, a yellow filter of a transmissionwavelength range corresponding to yellow light and a magenta filter of atransmission wavelength range corresponding to magenta light.

This renders it possible to match and optimize characteristics of thetristimulus color filter and complementary color filters, provided onthe color liquid crystal display panel, and those of the light emittingdiodes for emitting three prime colors and the complementary colorfilter, provided on the backlight device, such as to enlargesignificantly the color reproducing range of the picture demonstrated onthe color liquid crystal display.

Other objects and specified advantages of the present invention willbecome more apparent from the following explanation of preferredembodiments thereof which will now be made conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing spectral characteristics of a color filter ofa color liquid crystal display panel provided on a conventional colorliquid crystal display apparatus.

FIG. 2 is a graph showing the spectrum of a light source (CCFL) of thebacklight device provided in the color liquid crystal display apparatus.

FIG. 3 is a graph showing the xy chromaticity diagram of the XYZ colorsystem, in which there is additionally shown the color reproducing rangeof the conventional color liquid crystal display apparatus, employingthe CCFL as light source for the backlight device.

FIG. 4 is an exploded perspective view showing a color liquid crystaldisplay apparatus embodying the present invention.

FIG. 5 is a plan view showing a color filter of a color liquid crystaldisplay panel constituting a color liquid crystal display apparatus.

FIG. 6 is a perspective view showing a backlight device constituting acolor liquid crystal display apparatus.

FIG. 7 is a block circuit diagram showing a driving circuit for drivinga color liquid crystal display apparatus.

FIG. 8 is a graph showing the Pointer's Color.

FIG. 9 is a graph showing the color reproducing range of the sRGBstandard.

FIG. 10 is a graph showing the color reproducing range of the Adobe RGBstandard.

FIG. 11 is a graph showing the color reproducing range of the Pointerstandard.

FIG. 12 is a graph showing spectral characteristics of a color filter,having the NTSC ratio of the order of 100%, and those of the lightemitting diodes.

FIG. 13 is a graph for illustrating the visibility.

FIG. 14 is a graph showing spectral characteristics of a color filterand the spectra of light emitted from each light emitting diode in casethe peak wavelength of the blue light emitting diode is varied.

FIG. 15 is a graph showing the color gamut after the peak wavelength hasbeen changed and the color gamut before the peak wavelength is changed,for the case where the peak wavelength of the blue light emitting diodeis varied.

FIG. 16 is a graph showing spectral characteristics of the color filterand the spectra of light emitted from respective light emitting diodes,for the case where the peak wavelength of the blue light emitting diodeis varied.

FIG. 17 is a graph showing the color gamut after the peak wavelength hasbeen changed and the color gamut before the peak wavelength is changed,for the case where the peak wavelength of the blue light emitting diodeis varied.

FIG. 18 is a graph showing the color reproducing range in case the colorfilter has been improved.

FIG. 19 is a graph showing the color gamut of the blue (B) region incase the color filter has been improved.

FIG. 20 is a graph showing the color gamut of the green (G) region incase the color filter has been improved.

FIG. 21 is a graph showing the color gamut of the red (R) region in casethe color filter has been improved.

FIG. 22 is a graph showing the measured results of FIG. 17 in terms ofthe dependency of the NTSC ratio on the wavelength of the blue lightemitting diode.

FIG. 23 is a graph showing the spectral characteristics of the colorfilter and the blue light emitting diode in case of shifting of the bluelight emitting diode and the blue filter towards the short wavelengthside.

FIG. 24 is a graph showing the dependency of the NTSC ratio on thewavelength of the blue light emitting diode in case of shifting of theblue light emitting diode and the blue filter towards the shortwavelength side.

FIG. 25 is a graph showing the color reproducing range in case ofshifting of the blue light emitting diode and the blue filter towardsthe short wavelength side.

FIG. 26 is a graph showing the color gamut of the blue (B) region incase of shifting of the blue light emitting diode and the blue filtertowards the short wavelength side.

FIG. 27 is a graph showing the color gamut of the green (G) region incase of shifting of the blue light emitting diode and the blue filtertowards the short wavelength side.

FIG. 28 is a graph showing the color gamut of the red (R) region in caseof shifting of the blue light emitting diode and the blue filter towardsthe short wavelength side.

FIG. 29 is a graph showing the spectral characteristics of the colorfilter and the red light emitting diode in case the red light emittingdiode has been shifted towards the long wavelength side.

FIG. 30 is a graph showing the dependency of the NTSC ratio on thewavelength of the red light emitting diode in case the red lightemitting diode has been shifted towards the long wavelength side.

FIG. 31 is a graph showing the color reproducing range in case the redlight emitting diode has been shifted towards the long wavelength side.

FIG. 32 is a graph showing the color gamut of the of the blue (B) regionin case the red light emitting diode has been shifted towards the longwavelength side.

FIG. 33 is a graph showing the color gamut of the green (G) region incase the red light emitting diode has been shifted towards the longwavelength side.

FIG. 34 is a graph showing the color gamut of the of the red (R) regionin case the red light emitting diode has been shifted towards the longwavelength side.

FIG. 35 is a graph showing spectral characteristics of the color filterand the light emitting diodes in case of narrowing down the half-valuewidth of the green filter.

FIG. 36 is a graph showing the NTSC ratio plotted against the changes inthe half-value width of the green filter.

FIG. 37 is a graph showing the color reproducing range in case ofnarrowing down the half-value width of the green filter.

FIG. 38 is a graph showing the color gamut of the blue (B) region incase of narrowing down the half-value width of the green filter.

FIG. 39 is a graph showing the color gamut of the green (G) region incase of narrowing down the half-value width of the green filter.

FIG. 40 is a graph showing the color gamut of the red (R) region in caseof narrowing down the half-value width of the green filter.

FIG. 41 is a graph showing the spectral characteristics of a newlyimproved color filter and those of the light emitting diodes.

FIG. 42 is a graph showing the color reproducing range in case of usingthe newly improved color filter.

FIG. 43 is a graph showing the spectral characteristics of a newlyimproved color filter and those of newly optimized light emittingdiodes.

FIG. 44 is a graph showing the color gamut of the blue (B) color regionin case of using the newly improved color filter shown in FIG. 41 andthe newly optimized light emitting diodes.

FIG. 45 is a graph showing the color gamut of the green (G) region incase of using the newly improved color filter shown in FIG. 41 and thenewly optimized light emitting diodes.

FIG. 46 is a graph showing the color gamut of the red (R) region in caseof using the newly improved color filter shown in FIG. 41 and the newlyoptimized light emitting diodes.

FIG. 47 is a graph showing the Pointer's Color present in cyan andyellow regions.

FIG. 48 is a graph showing the vicinity of the cyan region of the colorreproducing range shown in FIG. 47.

FIG. 49 is a graph showing the vicinity of the yellow region of thecolor reproducing range shown in FIG. 47.

FIG. 50 is a graph for illustrating the limit of improvement for thetristimulus color filter and light emitting diodes for emitting threecolors.

FIG. 51 is a diagrammatic view for illustrating the results of count ofthe Pointer's Color present in cyan, yellow and magenta regions from onecolor reproducing range to another.

FIG. 52 is a diagrammatic view showing the constitution of a colorfilter added by a cyan filter.

FIG. 53 is a perspective view showing the constitution of a backlightdevice in which a cyan light emitting diode is added to the lightsource.

FIG. 54 is a graph showing spectral characteristics of a light sourceadded by a cyan light emitting diode.

FIG. 55 is a graph showing spectral characteristics of a color filteradded by a cyan filter.

FIG. 56 is a graph showing the color reproducing range in case ofaddition of the cyan filter and the cyan light emitting diode.

FIG. 57 is a graph showing the color gamut of the blue (B) region incase of addition of the cyan filter and the cyan light emitting diode.

FIG. 58 is a graph showing the color gamut of the green (G) region incase of addition of the cyan filter and the cyan light emitting diode.

FIG. 59 is a graph showing the color gamut of the red (R) region in caseof addition of the cyan filter and the cyan light emitting diode.

FIG. 60 is a graph showing the vicinity of the cyan region of the colorreproducing range shown in FIG. 56.

FIG. 61 is a graph showing the vicinity of the yellow region of thecolor reproducing range shown in FIG. 56.

FIG. 62 is a diagrammatic view showing the constitution of a colorfilter added by a cyan filter and a yellow filter.

FIG. 63 is a graph showing spectral characteristics of a light sourceadded by a cyan light emitting diode.

FIG. 64 is a graph showing a color filter added by a cyan filter and ayellow filter.

FIG. 65 is a graph showing the color reproducing range in case ofaddition of a cyan filter, a yellow filter and a cyan light emittingdiode.

FIG. 66 is a graph showing the color gamut of a blue (B) region in caseof addition of a cyan filter, a yellow filter and a cyan light emittingdiode.

FIG. 67 is a graph showing the color gamut of the green (G) region incase of addition of a cyan filter, a yellow filter and a cyan lightemitting diode.

FIG. 68 is a graph showing the color gamut of the red (R) region in caseof addition of a cyan filter, a yellow filter and a cyan light emittingdiode.

FIG. 69 is a graph showing the vicinity of the cyan region of the colorreproducing range shown in FIG. 63.

FIG. 70 is a graph showing the vicinity of the yellow region of thecolor reproducing range shown in FIG. 63.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, preferred embodiments of the presentinvention will be described in detail.

It should be noted that the present invention is not to be limited tothe embodiments now explained and may be optionally modified withoutdeparting from the scope of the invention.

The present invention is applied to, for example, a color liquid crystaldisplay apparatus 100 configured as shown in FIG. 4.

In this figure, the transmissive color liquid crystal display apparatus100 is made up of a transmissive color liquid crystal display panel 10,and a backlight unit 40, provided on the backside of this color liquidcrystal display panel 10. This transmissive color liquid crystal displayapparatus 100 may be provided with a receiving unit, such as an analogtuner or a digital tuner, for receiving the ground wave or the satellitewave, a picture signal processing unit or an audio signal processingunit for processing picture signals or audio signals, received by thisreceiving unit, respectively, and an audio signal outputting unit, suchas loudspeaker, for outputting audio signals processed by the audiosignal processing unit, although these units are not shown.

The transmissive color liquid crystal display panel 10 is made up of twotransparent substrates, formed by glass or the like (a TFT substrate 11and a counter-electrode substrate 12), and a liquid crystal layer 13 of,for example twisted nematic (TN) liquid crystal, enclosed in a spacebetween the two substrates. On the TFT substrate 11, there are formedsignal lines 14 and scanning lines 15, arranged in a matrixconfiguration, as well as thin-film transistors 16, as switchingelements, and pixel electrodes 17, arranged at the points ofintersection of the signal lines 14 and the scanning lines 15. Thethin-film transistors 16 are sequentially selected by the scanning lines15 to write picture signals, supplied from the signal lines 14, inassociated ones of the pixel electrodes 17. On the inner surface of thecounter-electrode substrate 12, there are formed counter electrodes 18and a color filter 19.

The color filter 19 will now be described. The color filter 19 isdivided into a plural number of segments each associated with a pixel.For example, the color filter is divided into three segments, associatedwith three prime colors, that is, a red filter CFR, a green filter CFGand a blue filter CFB, as shown in FIG. 5. The arraying pattern for thecolor filter may be exemplified by delta array or square array, notshown, in addition to the striped array shown in FIG. 5. The colorfilter 19 will be described in detail subsequently.

With the transmissive color liquid crystal display apparatus 100, thetransmissive color liquid crystal display panel 10 is sandwiched betweena pair of polarizing plates 31, 32, and driven in accordance with anactive matrix system, as white light is illuminated from its backside bythe backlight unit 40, such as to display a desired full-color picture.

The backlight unit 40 illuminates the color liquid crystal display panel10 from its backside. Referring to FIG. 4, the backlight device forcolor liquid crystal display 40 includes a backlight device 20, and aset of optical sheets, stacked on a light radiating surface 20a of thebacklight device 20, such as a light diffusing sheet 41, a prism sheet42 and a polarized light transforming sheet 43. The backlight device 20mixes the light from the light sources to generate white light which isradiated by surface light emission from a light radiating surface 20 a.

The set of optical sheets is made up of a plural number of sheets havingthe functions of resolving the incident light into mutuallyperpendicular polarized components, compensating the phase difference oflight waves to assure a broad angle of visibility and of preventingcoloration, diffusing the incident light and improving the luminance.The set of optical sheets is provided for transforming the light,radiated by surface light emission from the backlight device 20, intothe illuminating light having optimum optical characteristics forilluminating the color liquid crystal display panel 10. Consequently,the set of optical sheets may include not only the light diffusing plate41, prism sheet 42 or polarized light transforming sheet 43, but avariety of other optical sheets having other optical functions.

FIG. 6 depicts the configuration of the backlight device 20 in aschematic perspective view. Referring to FIG. 6, the backlight device 20uses, as light sources, a red light emitting diode 21R, radiating redlight, a green light emitting diode 21G, radiating green light, and ablue light emitting diode 21B, radiating blue light. In the followingdescription, in case the red light emitting diode 21R, green lightemitting diode 21G and the blue light emitting diode 21B are referred togenerically, each light emitting diode is simply referred to as lightemitting diode 21.

Referring to FIG. 6, a plural number of light emitting diodes 21 arearrayed in a line in a desired sequence to form a light emitting diodeunit 21 n, where n is a natural number. The sequence of arraying thelight emitting diodes on a substrate 22 is such that plural green lightemitting diodes 21G are arrayed at an equal distance from one anotherand plural red light emitting diodes 21R and blue light emitting diodes21B are alternately arrayed in the interstices between the neighboringgreen light emitting diodes 21G, as shown in FIG. 6.

A plural number of the light emitting diode 2 in are arrayed in abacklight housing 23, which is to be a backlight enclosure of thebacklight device 20, depending on the size of the color liquid crystaldisplay panel 10 adapted to be illuminated by the backlight unit 40.

The light emitting diode units 21 n may be arrayed in the backlighthousing 23 so that the longitudinal direction of the light emittingdiode units 2 in will be the horizontal direction, as shown in FIG. 6.Alternatively, the light emitting diode units 2 in may be arrayed sothat the longitudinal direction of the light emitting diode units 2 inwill be the vertical direction, in a manner not shown, or so that thelongitudinal direction of the light emitting diode units 2 in will bepartly the horizontal direction and partly the vertical direction.

The technique of arraying the light emitting diode units 21 n so thatthe longitudinal direction thereof will be the horizontal direction orthe vertical direction is equivalent to that of arraying the fluorescenttubes so far used preferentially as light sources of the backlightdevice. Thus, the accumulated designing know-how may be used to reducethe cost or manufacture time.

The light beams, radiated from the red light emitting diode 21R, greenlight emitting diode 21G and the blue light emitting diode 21B, aremixed together in the backlight housing 23 to create white light. Itshould be noted that a lens, a prism or a reflective mirror, forexample, is provided for each light emitting diode 21 so that the redlight, green light and blue light, radiated from each light emittingdiode 21, will be evenly mixed together in the backlight housing 23 tocreate radiated light of wide directivity.

Within the backlight housing 23, there are provided a diverter plate,not shown, having the color mixing function of mixing the light of therespective colors, radiated from the light emitting diodes 21, as lightsources, to create white light suffering from only little colorunevenness, and a diffusing plate for internal light diffusion forsurface emission of white light radiated from the diverter plate.

The white light, generated on color mixing by the backlight housing 20,is illuminated to the color liquid crystal display panel 10 via the setof optical sheets described above.

The color liquid crystal display apparatus 100 is driven by a drivingcircuit 200 shown for example in FIG. 7.

This driving circuit 200 includes a power supply unit 110 for supplyingdriving supply power for e.g. the color liquid crystal display panel 10and the backlight device 20, and an X-driver circuit 120 as well as aY-driver circuit 130 for driving the color liquid crystal display panel10. The driving circuit also includes an RGB processor 150, supplied viaan input terminal 140 with picture signals received by a receiver, notshown, of the color liquid crystal display apparatus 100, and which areprocessed by a picture signal processor. The driving circuit alsoincludes a picture memory 160 and a controller 170, both connected tothe RGB processor 150, and a backlight driving controller 180 fordriving controlling the backlight device 20 of the backlight unit 40.

In this driving circuit 200, the picture signals, transmitted as inputvia input terminal 140, are subjected to e.g. chroma processing, by theRGB processor 150, and converted from the composite signals into RGBseparate signals, for convenience in driving the color liquid crystaldisplay panel 10. The resulting signals are transmitted to thecontroller 170, while being transmitted via picture memory 160 to theX-driver circuit 120.

The controller 170 controls the X-driver circuit 120 and the Y-drivercircuit 130, at a preset timing, as matched to the RGB separate signals,in order to drive the color liquid crystal display panel 10 by RGBseparate signals, supplied via picture memory 160 to the X-drivercircuit 120, so as to display a picture corresponding to the RGBseparate signals.

The backlight driving controller 180 generates pulse-width modulatedsignal (PWM signal) from the voltage supplied from the power supply unit110 to drive respective light emitting diodes 21 operating as lightsources for the backlight device 20. In general, the color temperatureof a light emitting diode depends on the operating current. Thus, ifdesired to faithfully reproduce the color (to render the colortemperature constant) as desired luminance is procured, it is necessaryto drive the light emitting diode 21, using the PWM signal, to suppressvariations in color.

A user interface 300 is an interface for selecting a channel received bythe aforementioned receiving unit, not shown, adjusting the volume ofaudio output from an audio output unit, not shown, and for adjusting thewhite balance or the luminance of white light from the backlight device20 adapted for illuminating the color liquid crystal display panel 10.

For example, if the user has adjusted the luminance from the userinterface 300, a luminance control signal is transmitted to thebacklight driving controller 180 via controller 170 of the drivingcircuit 200. The backlight driving controller 180 is responsive to thisluminance control signal to vary the duty ratio of the PWM signal foreach of the red light emitting diode 21R, green light emitting diode 21Gand the blue light emitting diode 21B to effect driving control of thered light emitting diode 21R, green light emitting diode 21G and theblue light emitting diode 21B.

The color liquid crystal display apparatus 100, configured as describedabove, enlarges the color reproducing range of a picture displayed onthe color liquid crystal display panel 10 by matching, by way ofoptimization, the characteristics of the red filter CFR, green filterCFG and the blue filter CFB, provided on the color liquid crystaldisplay panel 10, to those of the light emitting diodes 21R, 21G and21B, provided on the backlight device 20.

Meanwhile, in a display device used for a computer monitor or a TVreceiver, there are a variety of standards for the color reproducingrange, as described above. In general, designing of the color filter 19or selection of the light emitting diodes 21 is made in order to achievethe color reproducing range complying with one of these standards. Inthe color liquid crystal display apparatus 100, shown as an embodimentof the present invention, designing of the color filter 19 or selectionof the light emitting diodes 21 is made to conform to a new colorreproducing range, which is a further extension of the Adobe RGBstandard, as the standard for the color reproducing range used inPhotoshop, an application software product prepared by Adobe SystemInc., by way of optimization.

The Adobe RGB standard provides a color reproducing range broader thanthe sRGB standard and, although it is not the international referencestandard, it has been accepted as the de facto standards for businessuse, such as printing/ publishing. This Adobe RGB standard has come tobe applied by reason of increased demand for monitoring colorreproduction of printed matter with the use of a large-sized display.

FIG. 8 shows 786 colors of the Pointer's Color on an xy chromaticitydiagram. The Pointer's Color, shown in FIG. 8, is a color chart whichhas extracted 786 surface colors existing in nature, on the basis of theMunsell color system (color chart). It may be said that this Pointer'sColor, if expressed, is expressing substantially the totality of thecolors that may be recognized by the human being.

FIG. 9 is a chart showing how much the Pointer's Color shown in FIG. 8is covered by the color reproducing range of the sRBG standard usedconventionally in prescribing the color reproducing range of thedisplay. In FIG. 9, there is also shown the XYX color system prescribedby the Commission Internationale de l'Eclairage (CIE). As may be seenfrom FIG. 9, the color reproducing range of the sRGB standard isappreciably narrower than that of the Pointer's Color. Calculations ofto which extent the color reproducing range of the sRGB standard coversthe Pointer's Color give a value equal to approximately 55%, meaningthat the sRGB standard expresses only about 55% of actually existingcolors.

FIG. 10 shows a chart corresponding to the chart of FIG. 9 added by thecolor reproducing range of the Adobe EGB standard. As may be seen fromFIG. 10, the color reproducing range of the RGB standard substantiallyencompasses the Pointer's Color. Calculations of how much the colorreproducing range of the Adobe RGB standard covers the Pointer's Colorgive a value equal to approximately 80%, meaning that the Adobe RGBstandard expresses only about 80% of actually existing colors.

With the Adobe RGB standard, the Pointer's Color cannot be met, as shownin FIG. 10. In particular, the magenta region, centered about magenta(red purple color), which is one of three prime colors in artists'colors or printing ink and is a complementary color of green, cannot becovered. There is now proposed a standard which provides a new colorreproducing range extending the Adobe RGB standard for complementing themagenta region, as shown in FIG. 11. The new color reproducing range,shown in FIG. 11, covers the Pointer's Color more extensively than theAdobe RGB standard. Calculations of how much the new color reproducingrange covers the Pointer's Color give a value equal to approximately90%. This new standard, providing the color reproducing range, which hasextended the Adobe RGB, is termed the Pointer standard, because itapproximately covers the Pointer's Color.

In the color liquid crystal display apparatus 100 embodying the presentinvention, it is attempted to optimize the picture, displayed on thecolor liquid crystal display panel 10, by designing the color filter 19and selecting the respective light emitting diodes 21, so that the colorreproducing range is such as satisfies this Pointer standard.

In the color liquid crystal display apparatus 100 embodying the presentinvention, it is necessary to maintain spectral intensity so that thewhite light radiated from the backlight device 20 corresponds to adesired color temperature to maintain the white balance.

For example, in the color liquid crystal display apparatus 100, thewhite balance of white light, radiated from the backlight device 20, isset such that its color temperature will be 10000±1000 K (Kelvin). Inorder for the color temperature of white light, radiated from thebacklight device 20, to be 10000±1000 K, it is necessary to set theintensity ratio of the peak wavelengths of the red light, green lightand blue light, emitted from the red light emitting diode 21R, greenlight emitting diode 21G and the blue light emitting diode 21B,respectively, not to 1:1:1, but to a preset ratio, changed from thissimple ratio, and to maintain the so changed ratio at all times in casethe characteristics of the light emitting diode 21 have been changed.

FIG. 12 shows spectral characteristics of a color filter 19 provided onthe color liquid crystal display panel 10 of the color liquid crystaldisplay apparatus 100 in case the color reproducing range is about equalto that of NTSC, that is, in case the NTSC ratio is approximately 100%.FIG. 12 also shows and corresponding spectral characteristics of thelight emitting diode 21. The color reproducing range about equal to theNTSC ratio is broader than the color reproducing range of theaforementioned sRCB, however, is narrower than the color reproducingrange of the Adobe RGB standard, to say nothing of the Pointer standard.

In the color liquid crystal display apparatus 100, embodying the presentinvention, the color reproducing range about the same as the NTSC ratiois used as a reference color reproducing range. Specifically, the colorreproducing range is such that, in case the peak wavelengths of the redlight emitting diode 21R, green light emitting diode 21G and the bluelight emitting diode 21B are 640 nm, 525 nm and 450 nm, respectively,for the red filter CFR with the peak wavelength Fpr=685 nm, the greenfilter CFG with the peak wavelength Fpg=530 nm and for the blue filterCFB with the peak wavelength Fpb=460 nm, the NTSC ratio is approximately100%, as shown in FIG. 12,

Since extending this color reproducing range to the Pointer standard istantamount to raising the color purity and providing for a broader colorgamut, it becomes crucial to lower the crossing points of the spectra ofrespective color light beams, radiated from the light emitting diodes21, and the transmission wavelength bands of the neighboring colorfilters 19, as indicated by circle marks in FIG. 12, and ultimately toreduce the crossing points to zero. This represents the fundamentaldesigning concept.

If desired to lower the crossing points, the peak wavelength of the redlight beam, radiated by the red light emitting diode, is ideallysituated as close to the long wavelength side as possible, with the peakwavelength of the green light, radiated by the green light emittingdiode, as center, to inhibit transmission of the red light beam throughthe green filter CFG. On the other hand, the peak wavelength of the bluelight beam, radiated by the blue light emitting diode 21B, is ideallysituated as close to the short wavelength side as possible, to inhibittransmission of the green light beam through the green filter CFG. Thecrossing points may similarly be lowered by narrowing the half-valuewidth of the green filter CFG to narrow its transmission wavelengthband.

However, the sensitivity to light of the human eye (visibility) differswith wavelengths, such that it reaches a peak value at 555 nm, becominglower towards the long wavelength side and towards the short wavelengthside, as shown in FIG. 13. In this figure, a visibility curve is shown,in which transmittance for 555 nm, which is at a peak value, isnormalized to unity (1).

Thus, if the peak wavelength of red light, radiated from the red lightemitting diode 21R, and that of the blue light, radiated from the lightemitting diode 21B, are shifted excessively towards the long wavelengthside or towards the short wavelength side, respectively, or thehalf-value width of the green filter CFG is reduced excessively, anextremely high power would be needed to raise the visibility which hasonce been lowered.

With this in view, the peak wavelength of red light, radiated from thered light emitting diode 21R, and that of the blue light, radiated fromthe light emitting diode 21B, may be shifted towards the long wavelengthside and towards the short wavelength side, respectively, or thehalf-value width of the green filter CFG may be reduced, in order tonarrow the transmission wavelength band of the green filter CFG such asto raise color purity to yield the desired color reproducing range, andsuch as to provide for a broader color gamut.

If, as the light emission intensity of each light emitting diode 21 ismaintained to keep up the desired proper white balance, the colorreproducing range of the color liquid crystal display apparatus 100 isto be enlarged to the Pointer standard, based on the aforementionedfundamental designing concept, the following concrete technique may nowbe proposed.

It is noted that, in the technique, now described, the display light,radiated from the color liquid crystal display panel 10 of the colorliquid crystal display apparatus 100, is measured with a colorimeter forall color gamuts.

EXAMPLE 1

Example in Which the Peak Wavelength λpb of the Blue Light EmittingDiode 21B is Shifted Towards the Short Wavelength Side

As described above, in case the peak wavelength λpb of the blue lightemitting diode 21B is shifted towards the short wavelength side, thecrossing point with the transmission wavelength band of the green filterCFG is lowered, and hence the color reproducing range becomes broader.

However, the red filter CFR exhibiting a certain value of transmittancein a wavelength region F in the vicinity of 400 nm to 450 nm of thewavelength of the transmission wavelength band of the blue filter CFB,as shown in FIG. 12, is obstructive in raising color purity or inproviding for a broader color gamut. For example, if the amount of lighttransmission of the red filter CFR is gradually increased from 450 nmtowards 400 nm until the red filter has the transmittance ofapproximately 12% at the wavelength of 400 nm, the respective colors aredeteriorated in color purity as a result of color mixing of the bluecolor light transmitted through the blue filter CFB and the red colorlight transmitted through the red filter CFR to interfere with enlargingthe color gamut, as shown in FIG. 12. This will now be verified.

It is assumed that the spectral characteristics of the color filter 19are such that, in the wavelength region F in the vicinity of 400 nm to450 nm of the transmission wavelength band of the blue filter CFB, thevalue of transmittance of red filter CFR is not zero, as shown in FIG.12. This color filter 19 is referred to below as a color filter 19Z. Itis also assumed that the peak wavelengths of the red light, green lightand blue light, radiated by the red light emitting diode 21R, greenlight emitting diode 21G and the blue light emitting diode 21B, as lightsources of the backlight device 20, respectively, are set such thatλpr=640 nm, λpg=525 nm and λpb=450 nm, in keeping with the spectralcharacteristics of the color filter 19Z shown in FIG. 12.

If the peak wavelengths of the light emitting diodes 21 are selected asdescribed above, a distance dl between the peak wavelength of the bluelight and that of the green light, as compared to a distance d2 betweenthe peak wavelength of the red light an that of the green light, is suchthat d1<d2, that is, the distance d1 is narrower than the distance d2.Thus, color mixing between the blue light and the green light tends tobe produced, such that color purity is worsened, and hence the colorgamut cannot be made broader.

It is now contemplated to use a blue light emitting diode 21B, in whichthe peak wavelength λpb of the emitted blue light has been shifted tothe side of a shorter wavelength, that is, in the direction indicated byarrow S in FIG. 12, to a side shorter in wavelength than 450 nm, by wayof changing the wavelength band. With the use of such blue lightemitting diode 21B, the distance dl becomes broader, so that colormixing between the blue light and the green light is less liable to beproduced, with the result that the color purity is improved, while thecolor gamut may be made broader.

In order that this may be verified, the color gamut in case the peakwavelength of the blue light emitting diode 21B has been shifted withrespect to the color filter 19Z having spectral characteristics shown inFIG. 12 is measured, and the peak wavelength, thus obtained, is comparedto the color gamut prior to shifting the peak wavelength. Specifically,the peak wavelengths of the red light emitting diode 21R and the greenlight emitting diode 21G are fixed, and several samples of the bluelight emitting diode 21B with respective different peak wavelengths areprovided. The color gamuts of the color filters, made up of these threesorts of the light emitting diodes, were measured as those blue lightemitting diode samples were interchanged.

FIG. 14 depicts a chart showing spectral characteristics of the colorfilter 19Z, also shown in FIG. 12, and wavelength spectra of the redlight, green light and blue light, radiated from the red light emittingdiode 21R, green light emitting diode 21G and the blue light emittingdiode 21B, respectively. It is noted that seven blue light emittingdiodes 21BN with the peak wavelengths of (460−5N) nm (N=0, 1, 2, . . . ,5, 6) were provided as the samples of the blue light emitting diodes21B.

Meanwhile, in FIG. 14, measurement is carried out beginning from theblue light emitting diode sample 21B of the peak wavelength λpb=460 nm,longer than 450 nm, in order that the effect of shifting the peakwavelength λpb of the blue light emitting diode 21B towards the shortwavelength side will be demonstrated more clearly.

FIG. 15 shows the results of the color gamut in case of using the bluelight emitting diodes 21BN with the peak wavelengths of (460−5N) nm. Asmay be seen from FIG. 15, the color gamut becomes broader than thepre-shift color gamut, on the green (G) and blue (B) sides, as the peakwavelength of the blue light emitting diodes 21B_(N) is shifted towardsthe shorter wavelength side. Conversely, the color gamut on the red (R)color side, expected to become broader than the pre-shift color gamut asthe peak wavelength of the blue light emitting diode 21B_(N) is shiftedtowards the short wavelength side, has become narrower. Specifically,the color gamut has become narrowest with the use of the blue lightemitting diode 21B₆ with the peak wavelength λpb=430 nm.

Based on the above results, the color gamut in case the peak wavelengthof the blue light emitting diode 21B has been shifted in the same way asdescribed above, for a color filter 19A, the spectral characteristics ofwhich are such that transmittance of the red filter CFR is set to zeroin the wavelength range F of 400 to 450 nm as shown in FIG. 12, wasmeasured and compared to the color gamut prior to shifting the peakwavelength.

FIG. 16 depicts a chart showing spectral characteristics of the colorfilter 19A, and wavelength spectra of the red light, green light andblue light, radiated from the red light emitting diode 21R, green lightemitting diode 21G and the blue light emitting diode 21B, respectively.It is noted that seven blue light emitting diodes 21B_(N) with the peakwavelengths of (460−5N) nm (N=0, 1, 2, . . . , 5, 6) were provided asthe samples of the blue light emitting diodes 21B.

Meanwhile, in FIG. 16, as in FIG. 14, measurement is carried outbeginning from the blue light emitting diode sample 21B of the peakwavelength λpb=460 nm, longer than 450 nm, for more clearlydemonstrating the effect of shifting the peak wavelength λpb of the bluelight emitting diode 21B towards the short wavelength side.

FIG. 17 shows the results of the color gamut in case of using the bluelight emitting diodes 21B_(N) with the peak wavelengths of (460−5N) nm.It may be seen from FIG. 15 that the color gamut becomes broader thanthe pre-shift color gamut, on the green (G) and blue (B) sides, as thepeak wavelength of the blue light emitting diodes 21B_(N) is shiftedtowards the shorter wavelength side. As for the color gamut of the red(R) color side, since the chromaticity point is not shifted in thedecreasing direction, the color gamut is not narrowed so severely withshift of the peak wavelength of the blue light emitting diodes 21B_(N)towards the short wavelength side, in a manner distinct from the case ofFIG. 15. Specifically, the color gamut becomes broadest with the use ofthe light emitting diode 21B₆ having the peak wavelength λpb=430 nm.

The results shown in FIG. 15 reflect the fact that, since the red filterCFR exhibits transmittance in the transmission wavelength band of theblue filter CFB, shown as a wavelength range F of the color filter 19Z,having spectral characteristics shown in FIG. 12, the red lighttransmitted through the red filter CFR is lowered in color purity. Theresults shown in FIG. 17 indicate the fact that, with the use of thecolor filter 19A, having the zero transmittance of the red filter CFRfor the wavelength range F of the color filter 19Z having the spectralcharacteristics shown in FIG. 12, the light incident on the red filterCFR is not transmitted through the red filter CFR in the same wavelengthrange as the transmission wavelength band of the blue filter CFR, withthe consequence that the red light transmitted through the red filterCFR becomes higher in color purity to moderate the above problem.

In FIG. 18, chromaticity points are plotted in the xy chromaticitydiagram for verifying how much the chromaticity points have beenimproved in the respective regions of red (R) color, green (G) color andblue (B) color, in case of using the blue light emitting diode 21Bhaving the peak wavelength λpb=450 nm. FIGS. 19 to 21 illustrate theregions of the red (R) color, green (G) color and the blue (B) color toan enlarged scale, respectively. Meanwhile, in the xy chromaticitydiagrams of FIGS. 18, 19, 20 and 21, there are also shown the Pointer'sColor, the color reproducing range of the sRGB standard, the colorreproducing range of the Adobe RGB standard, the color reproducing rangeof the Pointer standard and the XYZ color system prescribed by theCommission Internationale de l'Eclairage (CIE).

As may be seen in detail from FIGS. 19 to 21, there are no changes inthe chromaticity points in the regions of blue (B) color and green (G)color, however, in the region of the red (R) color, the chromaticitypoints have become broader than in the Pointer standard, thus testifyingto improvement. On the other hand, if the color filter 19Z is used, thechromaticity points are substantially the same in the red (R) region asthose provided for in the Pointer standard.

FIG. 22 shows dependency of the NTSC ratio on the peak wavelength of theblue light emitting diode 21B, as found from the color gamut of FIG. 15,as measured in case of using the color filter 19Z, with non-zerotransmittance of the red filter CFR in the wavelength range F in thevicinity of 400 nm to 450 nm in the transmission wavelength band of theblue filter CFB. FIG. 22 also shows dependency of the NTSC ratio on thepeak wavelength of the blue light emitting diode 21B as found from thecolor gamut of FIG. 17, as measured in case of using the color filter19A, with the zero transmittance of the red filter CFR in the wavelengthrange F in the vicinity of 400 nm to 450 nm.

If, in FIG. 22, attention is paid to the case of the peak wavelength λpbof 450 nm, it may be seen that the color filter 19A has been improvedover the color filter 19Z by approximately 2%, specifically, from 108%to 110%, in terms of the NTSC ratio.

By using a color filter, improved over the color filter 19Z in thetransmittance of the red filter CFR in the wavelength range F of 400 nmto 450 nm, it is possible to improve the NTSC ratio. FIG. 22 showsdependency of the NTSC ratio on the peak wavelength of the blue lightemitting diode 21B, for the color filter 19Y, with the transmittance of6% of the red filter CFR, at the wavelength of 400 nm, as shown in FIG.12. This color filter 19Y has been improved over the color filter 19Z byapproximately 1%, specifically, from 108% to 109%, in terms of the NTSCratio, for the peak wavelength λpb of 450 nm.

The color gamut of the region of the red (R) color has now been madewider by setting the transmittance of the red filter CFR in thetransmission wavelength band of the blue filter CFB to zero or to 6% orless, as described above. Thus, if, with the color filters 19A, 19Y,having red filters CFR, the peak wavelength λpb of the blue lightemitting diode 21B is shifted towards the short wavelength side forlowering the crossing point, the color purity may be raised further togive a wider color gamut. It is now contemplated to shift the bluefilter CFB to the short wavelength side, in keeping with the shifting ofthe peak wavelength λpb of the blue light emitting diode 21B towards theshort wavelength side.

In short, as the peak wavelength λpb of the blue light emitting diode21B is shifted by 10 nm towards the short wavelength side from 450 nm to440 nm, the peak wavelength Fpb of the blue filter CFB is also shiftedby 20 nm towards the short wavelength side from 460 nm to 440 nm, asshown in FIG. 23. In the description to follow, the color filter,corresponding to the color filter 19A, the blue filter CFB of which hasits peak wavelength Fpb set such that 440 nm≦Fpb≦460 nm, is termed acolor filter 19B.

FIG. 24 depicts a chart in which the NTSC ratio is plotted against thepeak wavelength λpb of the blue light emitting diode 21B. As may be seenfrom FIG. 24, the NTSC ratio has been improved from 110% for the case ofusing the color filter 19A to 115%, that is, by 5%.

In FIG. 25, chromaticity points are plotted in the xy chromaticitydiagram for verifying how much the chromaticity points have beenimproved in the respective regions of red (R) color, green (G) color andblue (B) color, when the color filter 19B having the peak wavelengthFpb=440 nm is used, at the same time as the peak wavelength λpb of theblue light emitting diode 21B has been shifted to 440 nm. FIGS. 26 to 28illustrate the regions of the red (R) color, green (G) color and theblue (B) color to an enlarged scale, respectively. Meanwhile, in the xychromaticity diagrams of FIGS. 25 to 28, there are also shown thePointer's Color, the color reproducing range of the sRGB standard, thecolor reproducing range of the Adobe RGB standard, the color reproducingrange of the Pointer standard, the XYZ color system prescribed by theCommission Internationale de l'Eclairage (CIE), chromaticity points ofthe color filter 19Z and chromaticity points of the color filter 19A.

As may become clearer from FIGS. 26 to 28, there are no changes in thechromaticity points in the region of red (R) color, however, thechromaticity points in the region of the blue (B) color are appreciablyimproved. Specifically, it may be seen that the color gamut has becomeapproximately as broad as the Pointer standard, as the color reproducingrange of sRGB is covered. It may also be seen that, in the green (G)region, the color gamut has slightly become broader, because ofsuppression of the color mixing with the blue light emitting diode 21B.

That is, by setting the peak wavelength λpb of the blue light emittingdiode 21B such that 440 nm≦λpb≦450 nm, and by using the color filter19B, corresponding to the color filter 19A, the blue filter CFB of whichhas its peak wavelength Fpb set such that 440 nm≦Fpb≦460 nm, the colorreproducing range may be enlarged appreciably.

EXAMPLE 2

Example in Which the Peak Wavelength λpr of the Red Light Emitting Diode21R is Shifted Towards the Long Wavelength Side

As described above, in case the peak wavelength λpr of the red lightemitting diode 21R is shifted towards the long wavelength side, thecrossing point of the spectral curve with the transmission wavelengthband of the green filter CFG is lowered, and hence the color reproducingrange becomes broader.

Thus, as shown in FIG. 29, the peak wavelength λpr of the red lightemitting diode 21R is shifted towards the long wavelength side from 640nm by 5 nm, that is, to 645 nm, for the color filter 19B. FIG. 30 showshow the NTSC ratio is changed with changes in the peak wavelength λpr ofthe red light emitting diode 21R. It is seen from FIG. 30 that the NTSCratio has been changed to 116% from 115%, that is, the NTSC ratio hasbeen improved by 1%, for the case in which, with the use of the colorfilter 19B, the peak wavelength λpb of the blue light emitting diode 21Bhas been shifted to 440 nm.

In FIG. 31, chromaticity points are plotted in the xy chromaticitydiagram for verifying how much the chromaticity points have beenimproved in the respective regions of red (R) color, green (G) color andblue (B) color, when the color filter 19B is used, the peak wavelengthλpb of the blue light emitting diode 21B is shifted to 440 nm and thepeak wavelength λpr of the red light emitting diode 21R has been shiftedto 645 nm. FIGS. 32 to 34 illustrate the regions of the blue (B) color,green (G) color and the red (R) color to an enlarged scale,respectively. Meanwhile, in the xy chromaticity diagrams of FIGS. 31 to34, there are also shown the Pointer's Color, the color reproducingrange of the sRGB standard, the color reproducing range of the Adobe RGBstandard, the color reproducing range of the Pointer standard, the XYZcolor system prescribed by the Commission Internationale de l'Eclairage(CIE), chromaticity points of the color filter 19Z, chromaticity pointsof the color filter 19A and chromaticity points in case of using theblue light emitting diode 21B with the peak wavelength λpb=440 nm in thecolor filter 19B.

As may become clearer from FIGS. 32 to 34, there are no changes in thechromaticity points in the region of the blue (B) color or in the green(G) color, however, the chromaticity points are slightly improved in thered (R) region, while the Munsell region of the Pointer's Color iscovered. It should be noted that, at the current time point, it isextremely difficult, from the reason related with the manufacturetechnique, to make the peak wavelength λpr of the red light emittingdiode 21R longer than 645 nm. For enlarging the color gamut, it isessential to elongate the wavelength of the red light emitting diode 21Reven in time to come. It may be expected to improve the characteristicsof the light emitting diode itself. If the red light emitting diode 21R,elongated in wavelength beyond the peak wavelength λpr, is produced intime to come, the color gamut will be enlarged further.

That is, by setting the peak wavelength λpb of the blue light emittingdiode 21B such that 440 nm≦λpb≦450 nm, by using the color filter 19B,corresponding to the color filter 19A, the blue filter CFB of which hasits peak wavelength λpb set such that 440 nm≦Fpb≦460 nm, and by settingthe peak wavelength λpr of the red light emitting diode 21R such that640 nm≦λpr≦645 nm, the color reproducing range may be enlargedappreciably.

EXAMPLE 3

Example in Which the Half-Value Width of the Green Filter CFG is MadeNarrower to Make the Transmission Wavelength Band Narrower

As described above, in case the transmission wavelength band of thegreen filter CFG is made narrower, the crossing points of thetransmission wavelength band with the spectral curves of the red lightemitting diode 21R and the green light emitting diode 21G, are lowered,and hence the color reproducing range becomes broader.

That is, the half-value width Fhwg of the green filter CFG is narrowedby equal amounts from 100 nm to 80 nm from the long wavelength side andfrom the short wavelength side, as shown in FIG. 35. In the descriptionto follow, the color filter, in which the half-value width Fhwg of thegreen filter CFG of the color filter 19B is narrowed by equal amountsfrom the long wavelength side and from the short wavelength side suchthat 80 nm≦Fhwg≦100 nm, is termed a color filter 19C.

FIG. 36 shows the manner in which the NTSC ratio is changed with changesin the half-value width Fhwg of the green filter CFG. As may be seenfrom FIG. 36, the NTSC ratio has been changed to 120% from 116%, whichis a value for the case in which the color filter 19B is used and thepeak wavelengths of the blue light emitting diode 21B and the red lightemitting diode 21R are set such that λpb=440 nm and λpr=645 nm, andhence the NTSC ratio has been improved by 4%.

In FIG. 37, chromaticity points are plotted in the xy chromaticitydiagram for verifying how much the chromaticity points have beenimproved in the respective regions of red (R) color, green (G) color andblue (B) color, when the green filter CFG with Fhwg=80 nm is used, thepeak wavelength λpb of the blue light emitting diode 21B is shifted to440 nm and the peak wavelength λpr of the red light emitting diode 21Ris shifted to 645 nm. FIGS. 38 to 40 illustrate the regions of the blue(B) color, green (G) color and the red (R) color to an enlarged scale,respectively. Meanwhile, in the xy chromaticity diagrams of FIGS. 37 to40, there are also shown the Pointer's Color, the color reproducingrange of the sRGB standard, the color reproducing range of the Adobe RGBstandard, the color reproducing range of the Pointer standard, the XYZcolor system prescribed by the Commission Internationale de l'Eclairage(CIE), chromaticity points of the color filter 19Z, chromaticity pointsof the color filter 19A, chromaticity points in case of using the bluelight emitting diode 21B, with the peak wavelength λpb=440 nm, for thecolor filter 19B, and chromaticity points in case of using the bluelight emitting diode 21B, with the peak wavelength λpb=440 nm, and thered light emitting diode 21B, with the peak wavelength λpr=645 nm, forthe color filter 19B.

As may become clearer from FIGS. 38 to 40, there are no changes in thechromaticity points in the region of the blue (B) color or in the red(R) color, however, the chromaticity points are improved in the green(G) region and the color gamut is further enlarged, as the colorreproducing range of the Adobe RGB standard, that is, the colorreproducing range of the Pointer standard, is covered.

That is, the color filter 19C, in which the half-value width Fhwg of thegreen filter CFG of the color filter 19B is narrowed by equal amountsfrom the long wavelength side and from the short wavelength side suchthat 80 nm≦Fhwg≦100 nm, is used, while the peak wavelength λpb of theblue light emitting diode 21B is set such that 440 nm≦λpb≦450 nm and thepeak wavelength λpr of the red light emitting diode 21R is set such that640 nm≦λpr≦645 nm. This allows for further increasing the colorreproducing range.

It should be noted that, in case the half-value width Fhwg of the greenfilter CFG is narrowed, luminance may sometimes be lowered. In case theluminance is lowered in this manner, it may be advisable to raise thetransmittance of the green filter CFG, for example, in order to assuredesired luminance values.

EXAMPLE 4

Further Improvement in Color Filter 19

In the above Examples 1 and 3, improvement in the color filter 19 hasbeen explained. More specifically, in Example 1, as the peak wavelengthλpb of the blue light emitting diode 21B is shifted to the shorterwavelength side for lowering the crossing point with the green filterCFG, the transmission wavelength band of the blue filter CFB is shiftedto the short wavelength side, so that its peak wavelength will become440 nm from 460 nm, for lowering the crossing point with the green lightemitting diode 21G. In Example 3, the half-value width Fhwg of the greenfilter CFG is reduced by equal amounts on the short and long wavelengthsides from 100 nm to 80 nm, in order to narrow down the transmissionwavelength band of the green filter CFG, so as to lower the crossingpoint with the red light emitting diode 21R and the crossing point withthe blue light emitting diode 21B.

In Example 4, the color filter 19 is to be improved further for raisingcolor purity and for providing for a wider color gamut, to add to theabove improvements.

FIG. 41 shows spectral characteristics of the color filter 19 newlyimproved, and spectral characteristics of the light emitting diode 21.The spectral characteristics, shown by thick broken line in FIG. 41, arespectral characteristics of the color filter 19Z shown in FIG. 12. Thespectral characteristics, shown by thick solid line, are newly improvedspectral characteristics of the color filter 19Z, and the spectralcharacteristics, shown by thin solid line, are those of the respectivelight emitting diodes 21. The peak wavelengths of the blue lightemitting diode 21B and the red light emitting diode 21R are not shiftedto the short wavelength side and to the long wavelength side,respectively, as in the Examples 1 and 3, and are of the reference peakwavelengths shown in FIG. 12.

The blue filter CFB has its peak wavelength Fpb shifted by 20 nm from460 nm to 440 nm, so that its transmission wavelength band will beshifted to the short wavelength side, as may be seen from the spectralcharacteristics of the color filter 19, shown in FIG. 41.

The red filter CFR has its peak wavelength Fpr shifted by 5 nm from 685nm to 690 nm, so that its transmission wavelength band will be shiftedto the long wavelength side.

The green filter CFG has its half-value width Fhwg shifted by 10 nm from100 nm to 90 nm, so that only the transmission wavelength band on theshort wavelength side crossing the blue light emitting diode 21B will beshifted towards the long wavelength side. In addition, the overalltransmittance of the green filter CFG is raised by 15% to compensate fordecrease in the transmission wavelength band.

In the description to follow, a color filter in which the peakwavelength Fpb of the blue filter CFB of the color filter 19Z is setsuch that 440 nm≦Fpb≦460 nm, the peak wavelength Fpr of the red filterCFR is set such that 685 nm≦Fpr≦690 nm, the peak wavelength Fpg of thegreen filter CFG is set to 530 nm, and in which the half-value widthFhwg of the spectrum of the green filter is set, by narrowing thetransmission wavelength band on the short wavelength side, such that 90nm≦Fhwg≦100 nm, while the transmittance of the green filter CFG israised by 15%, is termed a color filter 19D.

In FIG. 42, the color reproducing range is shown in the xy chromaticitydiagram for verifying how much the chromaticity points have beenimproved in the respective regions of red (R) color, green (G) color andblue (B) color, with use of the color filter 19D, in which Fpb=440 nm,Fpg=530 nm and Fpr=690 nm, and Fhwg=90 nm, and in which thetransmittance of the green filter CFG is raised by 15%. Meanwhile, inthe xy chromaticity diagrams of FIG. 42, there are also shown the colorreproducing range of the Adobe RGB standard, the color reproducing rangeof the XYZ color system prescribed by the Commission Internationale del'Eclairage (CIE), and the chromaticity points of the color filter 19Z.

It is seen from FIG. 42 that, with the use of the color filter 19D, thecolor gamuts for the regions of the blue (B) color and the red (R) colorare broader than not only the color gamut for the sRGB standard but alsothan the color gamut of the Adobe RGB standard or that of the colorfilter 19Z.

That is, with the use of the color filter 19D, corresponding to thecolor filter 19Z, having the blue filter CFB, the peak wavelength ofwhich is such that 440 nm≦Fpb≦460 nm, having the red filter CFR, thepeak wavelength Fpr of the which is such that 685 nm≦Fpr≦690 nm, andhaving the green filter CFG, the peak wavelength Fpg of which is 530 nm,with the half-value width Fhwg of the spectrum of the green filter beingset, by narrowing the transmission wavelength band on the shortwavelength side, such that 90 nm≦Fhwg≦100 nm, with the transmittance ofthe green filter CFG being raised by 15%, it is possible to enlarge thecolor reproducing range appreciably.

It is however seen that, as in the case of the color filter 19Z, thecolor gamut of the region of the green color (G) cannot cover the colorgamut of the Adobe RGB standard. In the Example 5, now described, thispoint is improved and, additionally, the light emitting diode 21, havingcharacteristics of further enlarging the color gamut, is selected, byway of optimization.

EXAMPLE 5

Further Optimization of the Light Emitting Diode 21

FIG. 43 shows spectral characteristics of the aforementioned colorfilter 19Z, indicated by thick broken line, spectral characteristics ofthe color filter 19D, indicated by thick solid line, spectralcharacteristics of the light emitting diode 21, before optimization,indicated by fine broken line, and spectral characteristics of the lightemitting diode 21, after optimization, indicated by fine solid line.

Referring to FIG. 43, the peak wavelength λpb of the blue light emittingdiode 21B is shifted by 10 nm, specifically, from 450 nm to 440 nm,towards the short wavelength side, the peak wavelength λpg of the greenlight emitting diode 21G is shifted by 5 nm, specifically, from 525 nmto 530 nm, towards the short wavelength side, and the peak wavelengthλpr of the red light emitting diode 21R is shifted by 5 nm,specifically, from 640 nm to 645 nm, towards the long wavelength side.

The shifting by 10 nm of the blue light emitting diode 21B towards theshort wavelength side, and the shifting by 5 nm of the red lightemitting diode 21R towards the long wavelength side, are as describedabove with reference to the Examples 1 and 2. If, on the other hand, thegreen light emitting diode 21G, the peak wavelength λpg of which hasbeen shifted towards the long wavelength side, is used, the crossingpoint with the blue filter CFB may be lowered, because the distance d1between the peak wavelength λpb of the blue light emitting diode 21B andthe peak wavelength λpg of the green light emitting diode 21G isenlarged, as explained with reference to FIG. 12, and hence it ispossible to lower the crossing point with the blue filter CFB. Theresult is that it is possible to improve color purity and to enlarge thecolor gamut of the green region.

In FIGS. 44 to 46, the color reproducing range is indicated in the xychromaticity diagram for verifying how much the chromaticity points havebeen improved in the respective regions of red (R) color, green (G)color and blue (B) color, in case the color filter 19D is used and thelight emitting diode 21 is optimized as shown in FIG. 43. Meanwhile, inthe xy chromaticity diagrams of FIGS. 44 to 46, there are also shown thecolor reproducing range of the Adobe RGB standard, the color reproducingrange of the Pointer standard, the XYZ color system prescribed by theCommission Internationale de l'Eclairage (CIE), the color reproducingrange of the sRGB standard, the color reproducing range of the colorfilter 19Z and the chromaticity points of the color filter 19D.

As will become clearer from FIGS. 44 to 46, the color gamut for eachcolor region is enlarged. In particular, the region of the green (G)color, not improved in the Example 4, shown in FIG. 45, as well as theregion of the red (R) color, shown in FIG. 46, surpasses the colorreproducing range of the RGB standard.

The NTSC ratio at this time is 116%, appreciably higher than 105% whichis the value of the NTSC ratio in case of using the color filter 19Z.Moreover, the loss in luminance, ascribable to reducing the half-valuewidth of the green filter CFG to provide for wide color gamut, iscompensated by increasing the transmittance of the green light,exhibiting higher visibility, by 15%, and hence there is no risk oflowering the luminance.

That is, by using the color filter 19D, setting the peak wavelength λpbof the blue light emitting diode 21B such that 440 nm≦λpb≦450 nm,setting the peak wavelength λpr of the red light emitting diode 21R suchthat 640 nm≦λpr≦645 nm, and by setting the peak wavelength λpg of thegreen light emitting diode 21G such that 525 nm≦λpg≦530 nm, the colorreproducing range may further be enlarged appreciably.

With the color liquid crystal display apparatus 100, configured asdescribed above, the color reproducing range of a picture displayed onthe color liquid crystal display panel 10 may be enlarged by matchingthe characteristics of the red filter CFR, green filter CFG and the bluefilter CFB, provided on the color liquid crystal display panel 10, tothe characteristics of the light emitting diodes 21R, 21G and 21B,provided on the backlight device 20, by way of optimization.

[New Task]

FIG. 47 shows the color reproducing ranges, assembled together on an xychromaticity diagram, in case the color filter 19D, shown enlarged inFIGS. 44 to 46 for red (R), green (G) and blue (B), respectively, isused and the light emitting diodes 21 are optimized, as shown in FIG.43.

In the xy chromaticity diagram, shown in FIG. 47, there are also shownthe Pointer's Color, the color reproducing range of the sRGB standard,the color reproducing range of the Adobe RGB standard and the XYX colorsystem as provided for by the Commission Internationale de l'Eclairage(CIE).

Referring to FIG. 47, the color reproducing range may appreciably beenlarged such as to meet substantially the Adobe RGB standard, byemploying the color filter 19D, and by setting the peak wavelength λpbof the blue light emitting diode 21B, the peak wavelength λpr of the redlight emitting diode 21R and the peak wavelength λpg of the green lightemitting diode 21G to 440 nm≦λpb≦450 nm, 640 nm≦λpr≦645 nm and to 525nm≦λpg≦530 nm, respectively. However, it cannot be said that thePointer's Color is met fully. That is, even in case the color filter 19is improved, and the light emitting diodes 21 are optimized with respectto the improved color filter, to this extent, the colors existing aroundus cannot be represented completely.

The color reproducing range in case the color filter 19D, shown in FIG.47, is used, and the light emitting diodes 21 are optimized, cannotcover the cyan region C nor the yellow region Y. It is noted that thecyan region and the yellow region are centered about the cyan color(clear blue-green), as a complementary color to red (R) color, and aboutthe yellow color, as a complementary color to blue (B) color,respectively, and that the cyan and yellow colors are among three primecolors for paints or printing inks in the Pointer's Color.

It may be premeditated that improvement of the tristimulus color filter19, composed of the red filter CFR, green filter CFG and the blue filterCFB, or enlargement of the color reproducing range by proper selectionof the red light emitting diode 21R, green light emitting diode 21G andthe blue light emitting diode 21B, emitting three prime colors, asexplained in connection with the examples 1 to 5, are nearing theirlimits. Thus, even if attempts are made for further optimizing the colorfilter or the light emitting diodes, the point of saturation is reached,such that there is no prospect of enlarging the color reproducing rangefurther.

FIGS. 48 and 49 are graphs showing the vicinity of the cyan region C andthe yellow region Y, shown in FIG. 47, to an enlarged scale. As may beseen from FIGS. 48 and 49, the rate of coverage of the Pointer's Colorin the cyan region C is rather low. That is, the rate of the Pointer'scolor present in the cyan region C is higher than that in the yellowregion Y.

The broad color reproducing range, which will cover the Pointer's Colorcontained in the yellow region Y, becomes possible in case at least they-value in the xy chromaticity diagram is set such that y is equal to orlarger than 0.8.

However, the value of y of a chromaticity point Cmax, having the largesty-value that may be reached by improving the tristimulus color filter19, and the light emitting diodes 21, emitting red light, green lightand blue light, is of the order of 0.75, as shown in FIG. 50. Hence,even if the color reproducing range which covers Cmax is obtained, it isnot possible to completely cover the Pointer's Color in the cyan regionC or in the yellow region Y.

Meanwhile, in the chromaticity diagram of FIG. 50, there are also shownthe Pointer's Color, the color reproducing range of the sRGB standard,the color reproducing range of the Adobe RGB standard, the colorreproducing range of the Pointer standard and the XYZ color system asprescribed by the Commission Internationale de l'Eclairage (CIE).

In FIG. 51, there are shown count values of the numbers of points of thePointer's Color lying outside the color reproducing ranges, that is, thecolor gamuts, of the color filters 19A and 19D and the Adobe RGB, foreach of the cyan region C, yellow region Y and the magenta region M, andthe rate of coverage of the Pointer's Color for each of the colorfilters and the Adobe RGB.

For example, if an ideal color reproducing range, which will cover thetotality of the pointer's Color of the cyan region C and the yellowregion Y, is to be achieved by improving the tristimulus color filter19, and the light emitting diodes 21, emitting the red light, greenlight and the blue light, such color reproducing range will be such aone shown by Ri in FIG. 50. This color reproducing range cannot beimplemented because it surpasses the XYZ color system as prescribed byCIE, testifying to the limit of improvement of the tristimulus colorfilter 19 and the light emitting diodes 21 emitting the three primecolors.

In the embodiments, now described, such color reproducing range is to beimplemented which will cover the totality of the Pointer's Color throughimprovement which is not merely that for three prime colors, namely thered, green and blue colors, but which is that for the cyan, magenta andblue colors, as colors complementary for the three prime colors.

EXAMPLE 6

In the Example 6, improvement is to be made for the cyan light so as tocover the Pointer's Color of the cyan region C. Specifically, a cyanfilter CFC, as a complementary color filter, is added to the colorfilter 19D, and the resulting filter is set as a color filter 19E, asshown in FIG. 26. The peak wavelength Fpc of the cyan filter is set suchthat Fpc=475 nm.

The arraying pattern for the color filter 19E, having the cyan filterCFC, may be exemplified by a delta array or a square array, not shown,in addition to the striped array shown in FIG. 52. The color filter 19Emay also be of any currently known arraying pattern.

A cyan light emitting diode 21C, as a complementary light emittingdiode, is added to the light emitting diode unit 21 n, by way of varyingthe light source configuration, as shown in FIG. 53. The peak wavelengthC of the cyan light emitting diode is set to 475 nm (peak wavelengthλpc=475 nm).

The reiterative units of the red light emitting diode 21R, green lightemitting diode 21G and the blue light emitting diode 21B are not limitedto the array shown in FIG. 27 such that it may be of any array asdesired.

For example, a red light emitting diode 21R, having a peak wavelengthλpr=645 nm, a green light emitting diode 21G, having a peak wavelengthλpg =530 nm, a blue light emitting diode 21B, having a peak wavelengthλpb=440 nm, and a cyan light emitting diode 21C, having a peakwavelength λpc=475 nm, are used as light sources. The spectraldistributions of these light emitting diodes are shown in FIG. 54. Theratio of intensities of the peak wavelengths of red light, green light,blue light and cyan light is set such that the while balance of thewhite light will be 10000±1000 K (Kelvin), in terms of the colortemperature, as shown in FIG. 54.

As the color filter 19E, a red filter CFR, with a peak wavelengthFpr=690 nm, a green filter CFG, with a peak wavelength Fpg=530 nm, ablue filter CFB, with a peak wavelength Fpb=440 nm and a cyan filterCFC, with a peak wavelength Fpc=475 nm, are used as a color filter 19E.The spectral characteristics of the filters are shown in FIG. 55. It isnoted that transmittance of the cyan filter CFC is adjusted to providefor a maximum color coverage rate of the cyan region C.

With the use of the light emitting diodes 21, added by the cyan lightemitting diode 21C, and the color filter 19E, the color reproducingrange of the color liquid crystal display apparatus 100 is that shown inan xy chromaticity diagram shown in FIG. 56. The NTSC ratio is improvedup to 121%. FIGS. 57, 58 and 59 show the blue color (B), green color (G)and the red (R) color, to an enlarged scale, respectively. Although theluminance is decreased only slightly from 100% to 97%, this low drop inluminance may be sufficiently coped with by slightly raising the powerof the light emitting diodes 21 inclusive of the cyan light emittingdiode 21C.

As may be seen from FIGS. 57 to 59, the color gamut is enlarged for theregion of the blue (B) color, such that deeper blue color may berepresented. On the other hand, the Adobe RGB region is sufficientlycovered by the green (G) color region and the red (R) color region.

Meanwhile, in the xy chromaticity diagrams of FIGS. 56 to 59, there arealso shown the Pointer's Color, the color reproducing ranges of the sRGBstandard and the Adobe RGB standard, the XYZ color system as prescribedby the Commission Internationale de l'Eclairage (CIE) and the colorreproducing range in case the NTSC ratio is set to 116% by using thecolor filter 19D and the light emitting diodes 21 are optimized.

The NTSC ratio may appreciably be improved in this manner from 116% to121% by using the color filter 19E and the light emitting diodes 21added by the cyan light emitting diode 21C. However, from the magnifiedviews of the vicinity of the cyan region C and the yellow region Y,shown in FIGS. 30 and 61, it is seen that there is still the Pointer'sColor that remains to be covered. The rate of coverage of the Pointer'sColor, as measured, is on the order of 97.8%.

In the Example 7, now described, the coverage rate for the Pointer'scolor is to be improved further.

EXAMPLE 7

In the Example 6, improvement is directed to cyan light. So, in theExample 7 to follow, improvement is to be directed to yellow color.Specifically, a yellow filter CFY, as a complementary color filter, isadded to the color filter 19E, and the resulting filter is set as acolor filter 19F. The peak wavelength Fpy of the yellow filter CFY isset such that Fpy=575 nm.

The arraying pattern for the color filter 19F, having the yellow filterCFC, may be exemplified by a delta array or a square array, not shown,in addition to the striped array shown in FIG. 62. The color filter 19Emay also be of any currently known arraying pattern.

As for a light source, emitting yellow light, the intensity of the skirtpart where the light emission spectrum of the red light emitting diode21R intersects that of the green light emitting diode 21G suffices.Consequently, no yellow light emitting diode is used as a complementarylight emitting diode, and a cyan light emitting diode 21C is added tothe light emitting diode 21 n, by way of varying the light sourceconfiguration, as shown in FIG. 53. The peak wavelength λpc of the cyanlight emitting diode 21C is set to 475 nm (peak wavelength λpc=475 nm).

For example, a red light emitting diode 21R, having a peak wavelengthλpr=645 nm, a green light emitting diode 21G, having a peak wavelengthλpg=530 nm, a blue light emitting diode 21B, having a peak wavelengthλpb=440 nm, and a cyan light emitting diode 21C, having a peakwavelength λpc=475 nm, are used as light sources. The spectraldistributions of these light emitting diodes are those shown in FIG. 63.The ratio of intensities of the peak wavelengths of red light, greenlight, blue light and cyan light is set such that the white balance ofthe white light will be 10000±1000 K (Kelvin), in terms of the colortemperature, as shown in FIG. 54.

As the color filter 19F, a red filter CFR, with a peak wavelengthFpr=690 nm, a green filter CFG, with a peak wavelength Fpg=530 nm, ablue filter CFB, with a peak wavelength Fpb=440 nm, a cyan filter CFC,with a peak wavelength Fpc=475 nm, and a yellow filter CFY, with a peakwavelength Fpy=575 nm, are used. The spectral characteristics of thefilters are those shown in FIG. 64. It is noted that transmittance ofthe cyan filter CFC and that of the yellow filter CFY are adjusted toprovide for a maximum color coverage rate of the cyan region C and theyellow region Y. In particular, the yellow filter CFY is proximate tothe locus of the spectrum as indicated by the CIE standard color system,insofar as saturation is concerned, and hence no high light intensity isrequired. Thus, the transmittance of the yellow filter CFY is suppressedto as low a value as possible.

With the use of the light emitting diodes 21, inclusive of the cyanlight emitting diode 21C, and the color filter 19F, the colorreproducing range of the color liquid crystal display apparatus 100 isthat shown in an xy chromaticity diagram shown in FIG. 65. The NTSCratio is improved up to 125%. FIGS. 66, 67 and 68 show the blue color(B), green color (G) and the red (R) color, to an enlarged scale,respectively. Although the luminance is slightly decreased from 100% to89%, this drop in luminance, on the order of 10%, may be sufficientlycoped with by slightly raising the power of the light emitting diodes 21inclusive of the cyan light emitting diode 21C.

It is seen from FIGS. 66 to 68 that the color gamut is enlarged for theregion of the blue (B) color, such that deeper blue color may berepresented, and that the Adobe RGB region is sufficiently covered bythe green (G) color region and the red (R) color region.

Meanwhile, in the xy chromaticity diagrams of FIGS. 65 to 68, there arealso shown the Pointer's Color, the color reproducing ranges of the sRGBstandard and the Adobe RGB standard, the XYZ color system as prescribedby the Commission Internationale de l'Eclairage (CIE) and the colorreproducing range in case the NTSC ratio is set to 116% by using thecolor filter 19D and by optimizing the light emitting diodes 21.

Thus, by using the color filter 19F and the light emitting diodes 21,added by the cyan light emitting diode 21C, as light source, the NTSCratio may be improved appreciably from 116% to 125%. From the magnifiedviews of the vicinity of the cyan region C and the yellow region Y,shown in FIGS. 69 and 70, it is seen that the totality of the Pointer'sColor is included in the color reproducing range, with the coverage rateof the Pointer's color amounting to 100%.

Meanwhile, no yellow light emitting diode is used in Example 7. However,if this yellow light emitting diode is used, the equivalent effect ofaccomplishing the coverage rate of 100% of the Pointer's Color may beachieved as desired luminance is maintained. In the Examples 1 to 5, themagenta region M is enlarged to the Pointer standard without using acomplementary color filter or a complementary color light emittingdiode. Alternatively, the magenta region may be enlarged by using themagenta filter and the magenta light emitting diode.

Meanwhile, it is not essential to use all of the items of improvement ofthe respective color filters of the color filter 19 or all of theoptimized light emitting diodes 21, shown in the Examples 1 to 7, incombination. On the contrary, these items of improvement of therespective color filters or the optimized light emitting diodes may beused selectively or by themselves for enlarging the color reproducingrange.

In this manner, the Pointer's Color, equivalent to all colors existingaround us, may be met by 100%, by using complementary color lightemitting diodes, such as cyan light emitting diode 21C, yellow lightemitting diode or magenta light emitting diode, as light source, inaddition to the light emitting diodes, emitting three prime colors, thatis, red light emitting diode 21R, green light emitting diode 21G and theblue light emitting diode 21B, and also using a cyan filter CFC, ayellow filter CFY or a magenta filter CFM, in addition to thetristimulus filter, namely a red filter CFR, a green filter CFG and ablue filter CFB, as a color filter.

Hence, the color liquid crystal display apparatus 100, including thebacklight device 20, having such light source, and the color liquidcrystal display panel 10, having such color filter, is able to expresse.g. the emerald-colored sea, wine-red deep scarlet and deep green ofbudding trees, to a color close to natural color, thereby enlarging thecolor reproducing range significantly.

The color liquid crystal display apparatus 100, shown as examples of thepresent invention, is provided with a subjacent backlight device 20 inwhich the light source is arranged directly below the color liquidcrystal display panel 10. The present invention is not limited to thisconfiguration and similar favorable effects may be displayed in case ofusing an edge lit display in which the light from the light sourcearranged laterally of the light guide plate as a backlight device issubjected to color mixing by the light guide plate.

The present invention is not limited to the particular configurations ofthe embodiments described above with reference to the drawings. It willbe appreciated that the present invention may encompass various changesor corrections such as may readily be arrived at by those skilled in theart within the scope and the principle of the invention.

1. A color liquid crystal display apparatus including a transmissivecolor liquid crystal display panel, having a color filter, and abacklight device for illuminating said color liquid crystal displaypanel with white light from a backside thereof, said backlight devicecomprising: a light source made up of light emitting diodes emittingthree prime colors, namely a red light emitting diode, emitting redlight having a peak wavelength λpr such that 640 nm≦λpr≦645 nm, a greenlight emitting diode, emitting green light having a peak wavelength λpgsuch that 525 nm≦λpg≦530 nm, and a blue light emitting diode, emittingblue light having a peak wavelength λpb such that 440 nm≦λpb≦450 nm, andone or more of complementary color light emitting diodes including atleast one of a cyan light emitting diode, emitting cyan light, a yellowlight emitting diode, emitting yellow light and a magenta light emittingdiode, emitting magenta light; and color mixing means for mixing thecolor light emitted from said light source to generate white color,wherein said color filter includes a tristimulus color filter, made upof a red filter, a green filter and a blue filter; said red filterhaving a peak wavelength Fpr of a transmission wavelength range suchthat 685 nm≦Fpr≦690 nm, and having zero transmittance for thetransmission wavelength range of said blue filter; said green filterhaving a peak wavelength Fpg of a transmission wavelength range of 530nm and a half value width Fhwg of said transmission wavelength rangesuch that 80 nm≦Fhwg≦100 nm; said blue filter having a peak wavelengthFpb of a transmission wavelength range such that 440 nm≦Fpb≦460 nm, andsaid color filter further includes one or more complementary colorfilters including at least one of a cyan filter of a transmissionwavelength range corresponding to cyan light, a yellow filter of atransmission wavelength range corresponding to yellow light and amagenta filter of a transmission wavelength range corresponding tomagenta light.
 2. The color liquid crystal display apparatus accordingto claim 1 wherein a cyan light emitting diode, having a peak wavelengthrange λpc of 475 nm, is used as said complementary light emitting diode,and a cyan filter having a peak wavelength Fpc of a transmissionwavelength range of 475 nm.
 3. The color liquid crystal displayapparatus according to claim 1 wherein a yellow filter having a peakwavelength Fpy of a transmission wavelength range of 575 nm is used assaid complementary color filter.
 4. The color liquid crystal displayapparatus according to claim 1 wherein the half-value width Fhwg of thetransmission wavelength range of the green filter is set such that 80nm≦Fhwg≦100 nm by decreasing the transmittance of the green filter for atransmission wavelength range of said blue filter and for a transmissionwavelength of said red filter.
 5. The color liquid crystal displayapparatus according to claim 1 wherein the half-value width Fhwg of thetransmission wavelength range of the green filter is set such that 900nm≦Fhwg≦100 nm by decreasing the transmittance of the green filter forthe transmission wavelength range of said blue filter.
 6. The colorliquid crystal display apparatus according to claim 5 wherein thetransmittance of said green filter is raised by 15%.